In the planning of radio wave propagation for point-to-point, point-to multipoint connections as well as for area coverage applications etc., path profiles are today usually generated between specified endpoint coordinates, using raster format topography data, such as elevation, clutter, obstacles, etc. The quality of a generated path profile depends heavily on the quality of the input data sets, as well as the algorithms used. The main sources for uncertainties can be listed as follows:
Map projection. Approximations in the map projection will affect the azimuth and distance of the path profile. PA1 Topography data resolution. Uncertainties in the heights of obstacles and clutter will directly affect the data values of the path profile, as will uncertainties in the location or extent of obstacles. Using topography data with a resolution too low for the application at hand will also result in large uncertainties. PA1 Path profile generation algorithm. Approximations in the algorithm will affect the data values of the generated path profile. This includes intricate considerations for determining discrete endpoint coordinates, the direction in which to generate the profile, the interpolation method used to extract data from the raster, etc. PA1 First a primary path profile according to the prior art is generated. PA1 Thereupon a number of adjacent path profiles are generated. PA1 The generated adjacent path profiles are then transformed according to some suitable scheme onto the primary path profile, and PA1 The resulting path profile is used as planning input data. PA1 Each of the path profiles is kept as a separate entity. The path profile handling is modified to treat the full set of primary and adjacent path profiles. This implies that any calculation must be repeated for each path profile, and that any display or result presentation must accommodate more than one path profile, or, at worst, the whole set. The main advantage of this method is that it permits direct comparisons of the end results (signal levels, fade margins, quality measures, etc.) between primary and adjacent path profiles, or PA1 Each of the adjacent path profiles is merged with the primary path to produce a single, merged profile that can be used in exactly the same way as path profiles are currently being used in radio wave propagation planning. The main advantage of this method is that it only affects the path profile generation routine, and leaves the rest of the system unaffected, while still taking into account any adjacent obstacles in the generated path profiles. A slight drawback would be the performance loss due to the line-of-sight calculations required by the merging process.
The most desirable solution would be to completely eliminate all of these short-comings, but this is neither feasible nor possible. It is, however, possible to make the short-comings less significant.
Thus, topography data can be improved by means of simply increasing the resolution. This is always a good solution, but normally rather expensive. The vertical resolution of the topography data can be taken into account in the predictions. This will normally produce a more pessimistic result, which can be compared to the result obtained in a standard manner. Path profile generation algorithms can be made to use refined interpolation methods. This will normally be a good solution for non-urban areas, but will not eliminate the problems for urban areas, where obstacles tend to be discrete with respect to normal raster resolutions.
For example, a simple interpolation method is linear interpolation between the two closest raster points. This method is not very well suited for urban areas. Another method is selecting the highest of the two closest raster points. This method is better suited for urban areas, although constantly pessimistic. Yet another method is linear interpolation in the plane spanned by the three closest raster points. This method is not very well suited for urban areas.
Regardless of the path profile generation algorithm used, there will always remain some possibility for missing obstacles in the raster data, but this phenomenon will be less frequent for higher raster resolutions, or when using more sophisticated algorithms.